Rotary resistance with reduction gear



`uly 14,197() KHLER 3,520,207

` l ROTARY` RESISTANCE WITH REDUCTION GEAR Filed Dec. 5, 1968 lill-lin "7/1 'Llllilll IIIIIIIIIII United States Patent 3,520,207 ROTARY RESISTANCE WITH REDUCTION GEAR Josef Khler, Bad Neustadt an der Saale, Germany, as-

signor to Preh Electro-Feinmechanische Werke, Bad Neustadt an der Saale, Germany Filed Dec. 5, 1968, Ser. No. 781,483 Claims priority, applicatigltGrmany, Dec. 8, 1967,

U.S. Cl. 74-433 3 Claims ABSTRACT OF THE DISCLOSURE Rotary resistance with reduction gear having a wiper secured to a cup-shaped rotor embracing the stationary parts of the resistor and having the inner margin of the rotor provided with a ring gear, the latter being engaged by a stationary pinion arranged within the rotor. The outer surface of the peripheral wall of the cup-shaped rotor being formed as/or carrying a ring serving as a pulley for a scale cable.

The invention relates to a rotary resistance with reduction gear for the wiper movement. Such rotary resistors are used above all, when the resistance or the variable voltage or the current, respectively, should be adjustable finely as possible. Apart from the entire measuring and control technique in which such rotary resistors are customarily used, a new field of application is opened to them for tuning high-frequency circuits comprising variable capacitance diodes the blocking voltage of which for an exact station selection has to be easily and reproducibly adjustable within very narrow, mostly millivolt ranges. For this purpose it has been proposed already to provide a ygear wheel on the wiper shaft of a `customary rotary resistor and to drive the same by means of a pinion of suitable dimension. Such reduction gear is, however, very expensive and means a considerable increase of the price of the rotary resistor.

Apart from this, so-called rotary button or disk resistors are known having the wiper directly secured to the, rotary button serving for the adjustment or to a pulley driven by a cable.

The object of the present invention is to provide, starting out from such a disk resistor, a simplified and less expensive rotary resistor construction with reduction gear.

According to the present invention, it is proposed for the design of the reduction gear of a rotary resistor havingits wiper secured on a cupshaped rotor, the latter embracing the stationary parts of the rotary resistor, to provide the inner margin of the rotor with a gear engaging a drive pinion arranged within the rotor.

Since the gear ring may be formed on the rotor, the latter being injection molded or pressed of plastics, the formation of a separate driven element of the gear is eliminated. Due to the arrangement of the pinion within the rotor, the outer shape of the rotary resistor may be kept relatively small for a predetermined size of the resistance element, whereby its stability is increased. In such a design, the pitch circle of the driven element is but slightly smaller than the outer diameter of the entire rotary resistor resulting, even for a relatively large modulus, in a high number of teethv and wide limits for the selection of the reduction ratio.

In a preferable embodiment of the invention, the rotor is formed, in a manner known per se, as cable pulley serving for the support of a cable of a scale indicator.

3,520,207 Patented July 14, 1970 ICC Since the position of the scale indicator without any intermediate element depends directly on the angular position of the rotor, no transmission errors ycan occur with such a construction in regard to the indication.

For accommodating different length of scales, the rotor may also have means for the securement of an intermediate ring having its outer peripheral surface correspond for a given rotary path 0f the resistor to the desired length of the scale.

The invention and its details `will become more easily understood from the following description of one embodiment when read in connection with the accompanying drawings.

In the drawings:

FIG. 1 shows a section through a rotary resitsor with reduction gear; and

FIG. 2 shows a plan on the same rotary resistor.

Referring to the drawing, the carrier plate 1, consisting of a zink die casting, has formed thereon the bearing bushing 2 for rotary shaft 3 and a bushing 4 for drive shaft 5. Resistance element 6 is secured to carrier plate 1 by means of hollow rivets 7, & The resistance element consists of the circular insulating plate 9 to which the resitsance layer 10 is applied, such as by printing. The beginning and the end of resistance layer 10` is provided with soldering terminals 11, 12. A center tap, consisting of annular track 14 and soldering terminal 14, is secured on the insulating plate 9 with the interposition of an isolating annulus 13 by rivet pins 15.

The circular rotor 16, into the center of `which shaft 3 is injectionmolded by its knurled end, is formed as a shallow cup embracing the stationary parts of the rotary resistors. Wiper spring 17 is thermoplastically secured to the inner side of the bottom of the rotor. The wiper spring 17 has one arm resting on the center tap ring 14 and its other arm by carbon contact 18 on resistance layer 10.

A gear rim 19 is formed on the inner rim of rotor 16 over a range of approximately 300 degrees of its circumference. This gear rim 19 is engage by pinion 20, the latter being supported in bushing 4 of supporting plate 1 and axially retained by blocking ring 21. The diameter of the pitch circle of the pinion amounts to 1/3 of the diameter of the pitch circle of gear rim 19, resulting in a reduction of the wiper movement at the ration 1:3. The rotary movement of the rotor is limtied to 270 by abutments 22 in cooperation with rivet pins 15. For securement of the rotary resistors, a thread is formed on bushing 4 and plugs 23 are interiorly threaded.

The outside of rotor 16 is formed as a cylinder surface and serves for the reception of a rope or pulley 24 transforming the rotary movement of the rotor into a linear movement of the symbolically shown indicator 25.

For adapation to a greater scale length, a plastic annulus 26, indicated by dot-and-dash lines, may be placed on the rotor and thermoplastically secured to plugs 27 formed on the rotor 16.

While there has been described what at present is believed to be a preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, to cover in the appended claims all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. In a rotary resistor having a reduction gear and a wiper secured to a cup-shaped rotor embracing stationary parts of a resistance element, the improvement 3 of providing the inner rim of said rotor with a gear rim References Cited engaging a drive pinion provided within said rotor. UNITED'- STATES .PATENTS- 2. In a rotary resistor according to claim 1, the outer surface of said rotor according to claim 1, the outer surglln set alt' l"" face of said rotor being formed as a pulley for a Scale 5 3360757 12/1967 Wahlbeslgen e a' 338:162

cable.

3. In a rotary resistor according to claim 1 in which LEONARD H GERIN2 primary Examiner said rotor is provided `with means adapted for the securement of an annular member serving as cable pulley for I U.S. Cl. X.R. a scale cable. 10 338-116 

